The adrenal glands are endocrine glands which produce both glucocorticoid and mineralocorticoid hormones in response to critical illness. The primary glucocorticoid hormone is cortisol, whereas the primary mineralocorticoid hormone is aldosterone. Cortisol has important cardiovascular, metabolic, immunologic, and hemostatic functions. In comparison, aldosterone is important in salt and water regulation and therefore critical to the maintenance of intravascular volume and blood pressure. Acute adrenal insufficiency is the failure of the adrenal gland to respond appropriately to physiologic stress, such as infection. The clinical presentation of acute adrenal insufficiency is due to insufficient mineralocorticoid activity rather than inadequate glucocorticoid activity. As such, critically ill patients with acute adrenal insufficiency can present with low blood pressure and severe dehydration. Thus, it has been hypothesized that mineralocorticoid deficiency may contribute to the development and severity of septic shock. Although many researchers have studied the importance of glucocorticoid activity in septic shock, the importance of mineralocorticoid activity and aldosterone in septic shock remains unclear. Aldosterone is produced in the adrenal gland and causes increased renal sodium reabsorption via the activity of an amiloride-sensitive epithelial sodium (Na) channel (ENaC). Increased reabsorption of sodium leads to expansion of intravascular volume and increased blood pressure. Amiloride is a potassium sparing diuretic that blocks ENaC thereby inhibiting sodium reabsorption in the late distal convoluted tubules, connecting tubules, and collecting ducts in the kidney. Hydrochlorothiazide (HCT), a well described diuretic, will be used in conjunction with amiloride to ensure maximal effect on eNaC function. ENaC is expressed on the apical plasma membrane of many organs including the kidneys, lungs, urinary bladder, distal colon, sweat glands, and salivary ducts.1 For the purpose of this protocol, we will concentrate on the importance of ENaC in the kidneys and the lungs Using a canine model of septic shock, our lab has previously conducted experiments suggesting mineralocorticoid activity via aldosterone may be important to the pathophysiology of septic shock. We demonstrated that administration of desoxycorticosterone acetate (DOCA), a selective mineralocorticoid with physiologic effects similar to aldosterone given 72h before the onset of sepsis, led to a more rapid reversal of shock and improved survival. The direct effect on sodium reabsorption or ENaC activity was not measured in these experiments but these results suggest that the administration of DOCA leads to increased renal sodium reabsorption and preservation of intravascular volume resulting in less severe shock and improved survival. As a basic physiologic question, this study will expand our understanding of sodium channels in the kidney and lung and the role mineralocorticoids plays in managing fluid balance during critical illness. This study will also show how the expression of these channels can be influenced to improve survival. From a clinical perspective, if prophylactic treatment is shown to improve survival this would immediately benefit patients subject to high risk for infection surgical procedures, ie, abdominal. In addition, these results will define which components of the sodium channel could be targeted for drug development. This series of studies investigates the independent roles of glucocorticoids and mineralocorticoids in a sedated and ventilated model of sepsis. We began by defining normal adrenal function during sepsis in an ICU setting (Sweeney, JID 2010). We then determined the efficacy of selective corticosteroid agonists during sepsis (Hicks CCM 2012) and the role of corticosteroids on bacterial clearance (Hicks ICM 2012). We then investigated the Hypothalamic-Pituitary-Adrenal Axis in Lethal Canine Staphylococcus aureus Pneumonia (Corts-Puch AJP, 2014). The current study will expand our understanding of the mechanisms behind water handling and how survival is affected during critical illness